Were G2 lenses built for another camera?

Here is an excerpt taken from another forum about the G2 converter lenses:

-- hide signature --

"You can buy the Canon LA-DC58 adapter and mount a 58 mm filter on it.
But 58 mm is really oversize for this camera; Canon chose that size
so you could use the series of wide and tele and closeup adapters
that Canon already built for a different camera in that size. Apparently
the LA-DC58 can partially block the optical viewfinder and the focus
illuminator lamp."

I know the Canon adapter will partially block the viewfinder, but does anyone know if the other part of the above statement is TRUE? That is, did Canon go with a 58mm adapter so they could use lenses originally built for another camera? What other Canon camera (other than the G1) do these lenses work with?